Evaluation of Steel Bridges, Volumes I & II, TR-493, 2007

This report is divided into two volumes. This volume (Volume I) summarizes a structural health monitoring (SHM) system that was developed for the Iowa DOT to remotely and continuously monitor fatigue critical bridges (FCB) to aid in the detection of crack formation. The developed FCB SHM system enables bridge owners to remotely monitor FCB for gradual or sudden damage formation. The SHM system utilizes fiber bragg grating (FBG) fiber optic sensors (FOSs) to measure strains at critical locations. The strain-based SHM system is trained with measured performance data to identify typical bridge response when subjected to ambient traffic loads, and that knowledge is used to evaluate newly collected data. At specified intervals, the SHM system autonomously generates evaluation reports that summarize the current behavior of the bridge. The evaluation reports are collected and distributed to the bridge owner for interpretation and decision making. Volume II summarizes the development and demonstration of an autonomous, continuous SHM system that can be used to monitor typical girder bridges. The developed SHM system can be grouped into two main categories: an office component and a field component. The office component is a structural analysis software program that can be used to generate thresholds which are used for identifying isolated events. The field component includes hardware and field monitoring software which performs data processing and evaluation. The hardware system consists of sensors, data acquisition equipment, and a communication system backbone. The field monitoring software has been developed such that, once started, it will operate autonomously with minimal user interaction. In general, the SHM system features two key uses. First, the system can be integrated into an active bridge management system that tracks usage and structural changes. Second, the system helps owners to identify damage and deterioration.

Evaluation of a Bridge Constructed using High Performance Steel, May 2006

Of the approximately 25,000 bridges in Iowa, 28% are classified as structurally deficient, functionally obsolete, or both. Because many Iowa bridges require repair or replacement with a relatively limited funding base, there is a need to develop new bridge materials that may lead to longer life spans and reduced life-cycle costs. In addition, new and effective methods for determining the condition of structures are needed to identify when the useful life has expired or other maintenance is needed. Due to its unique alloy blend, high-performance steel (HPS) has been shown to have improved weldability, weathering capabilities, and fracture toughness than conventional structural steels. Since the development of HPS in the mid-1990s, numerous bridges using HPS girders have been constructed, and many have been economically built. The East 12th Street Bridge, which replaced a deteriorated box girder bridge, is Iowa’s first bridge constructed using HPS girders. The new structure is a two-span bridge that crosses I-235 in Des Moines, Iowa, providing one lane of traffic in each direction. A remote, continuous, fiber-optic based structural health monitoring (SHM) system for the bridge was developed using off-the-shelf technologies. In the system, sensors strategically located on the bridge collect raw strain data and then transfer the data via wireless communication to a gateway system at a nearby secure facility. The data are integrated and converted to text files before being uploaded automatically to a website that provides live strain data and a live video stream. A data storage/processing system at the Bridge Engineering Center in Ames, Iowa, permanently stores and processes the data files. Several processes are performed to check the overall system’s operation, eliminate temperature effects from the complete strain record, compute the global behavior of the bridge, and count strain cycles at the various sensor locations.

Audit report on Wave 2 of the Phase II Strategic Sourcing Initiative implemented by the Department of Administrative Services

Audit report on Wave 2 of the Phase II Strategic Sourcing Initiative implemented by the Department of Administrative Services

Back Warning Sensors for Tow Plows, RB07-012, 2013

Backup warning system devices were evaluated to determine if they would alert winter maintenance snow plow drivers to obstacles directly behind the trailer and out of view of the driver when a unit is backed up. When the sensors on the back of the tow plow were covered with snow during plowing operations, the sensor would go off in the cab and continue going off, which would result in drivers turning the volume of the unit way down. One shop stated that the wireless transmitted signal would be hit or miss depending on the winter weather that they were operating in. The sensors on the back of the tow plow trailer would come in contact with salt brine and in this situation one of the sensors did go bad. The weatherproof box that was designed to keep the system waterproof did not fully keep the moisture out. It was found that the system did alert drivers of items behind the unit and there were no backup accidents reported during the research period.

A Feasibility Study on Embedded Micro-Electromechanical Sensors and Systems (MEMS) for Monitoring Highway Structures, TR-575, 2011

Micro-electromechanical systems (MEMS) provide vast improvements over existing sensing methods in the context of structural health monitoring (SHM) of highway infrastructure systems, including improved system reliability, improved longevity and enhanced system performance, improved safety against natural hazards and vibrations, and a reduction in life cycle cost in both operating and maintaining the infrastructure. Advancements in MEMS technology and wireless sensor networks provide opportunities for long-term continuous, real-time structural health monitoring of pavements and bridges at low cost within the context of sustainable infrastructure systems. The primary objective of this research was to investigate the use of MEMS in highway structures for health monitoring purposes. This study focused on investigating the use of MEMS and their potential applications in concrete through a comprehensive literature review, a vendor survey, and a laboratory study, as well as a small-scale field study. Based on the comprehensive literature review and vendor survey, the latest information available on off-the-shelf MEMS devices, as well as research prototypes, for bridge, pavement, and traffic applications were synthesized. A commercially-available wireless concrete monitoring system based on radio-frequency identification (RFID) technology and off-the-shelf temperature and humidity sensors were tested under controlled laboratory and field conditions. The test results validated the ability of the RFID wireless concrete monitoring system in accurately measuring the temperature both inside the laboratory and in the field under severe weather conditions. In consultation with the project technical advisory committee (TAC), the most relevant MEMS-based transportation infrastructure research applications to explore in the future were also highlighted and summarized.

Assessment of Nondestructive Testing Technologies for Quality Control/Quality Assurance of Asphalt Mixtures, TR-653, 2015

Asphalt pavements suffer various failures due to insufficient quality within their design lives. The American Association of State Highway and Transportation Officials (AASHTO) Mechanistic-Empirical Pavement Design Guide (MEPDG) has been proposed to improve pavement quality through quantitative performance prediction. Evaluation of the actual performance (quality) of pavements requires in situ nondestructive testing (NDT) techniques that can accurately measure the most critical, objective, and sensitive properties of pavement systems. The purpose of this study is to assess existing as well as promising new NDT technologies for quality control/quality assurance (QC/QA) of asphalt mixtures. Specifically, this study examined field measurements of density via the PaveTracker electromagnetic gage, shear-wave velocity via surface-wave testing methods, and dynamic stiffness via the Humboldt GeoGauge for five representative paving projects covering a range of mixes and traffic loads. The in situ tests were compared against laboratory measurements of core density and dynamic modulus. The in situ PaveTracker density had a low correlation with laboratory density and was not sensitive to variations in temperature or asphalt mix type. The in situ shear-wave velocity measured by surface-wave methods was most sensitive to variations in temperature and asphalt mix type. The in situ density and in situ shear-wave velocity were combined to calculate an in situ dynamic modulus, which is a performance-based quality measurement. The in situ GeoGauge stiffness measured on hot asphalt mixtures several hours after paving had a high correlation with the in situ dynamic modulus and the laboratory density, whereas the stiffness measurement of asphalt mixtures cooled with dry ice or at ambient temperature one or more days after paving had a very low correlation with the other measurements. To transform the in situ moduli from surface-wave testing into quantitative quality measurements, a QC/QA procedure was developed to first correct the in situ moduli measured at different field temperatures to the moduli at a common reference temperature based on master curves from laboratory dynamic modulus tests. The corrected in situ moduli can then be compared against the design moduli for an assessment of the actual pavement performance. A preliminary study of microelectromechanical systems- (MEMS)-based sensors for QC/QA and health monitoring of asphalt pavements was also performed.

Comparison of Setting Time Measured Using Ultrasonic Wave Propagation with Saw-Cutting Times on Pavements, TR-675, 2015

At present, there is little fundamental guidance available to assist contractors in choosing when to schedule saw cuts on joints. To conduct pavement finishing and sawing activities effectively, however, contractors need to know when a concrete mixture is going to reach initial set, or when the sawing window will open. Previous research investigated the use of the ultrasonic pulse velocity (UPV) method to predict the saw-cutting window for early entry sawing. The results indicated that the method has the potential to provide effective guidance to contractors as to when to conduct early entry sawing. The aim of this project was to conduct similar work to observe the correlation between initial setting and conventional sawing time. Sixteen construction sites were visited in Minnesota and Missouri over a two-year period. At each site, initial set was determined using a p-wave propagation technique with a commercial device. Calorimetric data were collected using a commercial semi-adiabatic device at a majority of the sites. Concrete samples were collected in front of the paver and tested using both methods with equipment that was set up next to the pavement during paving. The data collected revealed that the UPV method looks promising for early entry and conventional sawing in the field, both early entry and conventional sawing times can be predicted for the range of mixtures tested.

IOWATER Sustaining the Wave

Summary of the IOWATER Program and workshops offered.

Seismic Wave Velocity as a Means of In-Place Density Measurement, Part 1, HR-114

Velocity-density tests conducted in the laboratory involved small 4-inch diameter by 4.58-inch-long compacted soil cylinders made up of 3 differing soil types and for varying degrees of density and moisture content, the latter being varied well beyond optimum moisture values. Seventeen specimens were tested, 9 with velocity determinations made along two elements of the cylinder, 180 degrees apart, and 8 along three elements, 120 degrees apart. Seismic energy was developed by blows of a small tack hammer on a 5/8-inch diameter steel ball placed at the center of the top of the cylinder, with the detector placed successively at four points spaced 1/2-inch apart on the side of the specimen involving wave travel paths varying from 3.36 inches to 4.66 inches in length. Time intervals were measured using a model 217 micro-seismic timer in both laboratory and field measurements. Forty blows of the hammer were required for each velocity determination, which amounted to 80 blows on 9 laboratory specimens and 120 blows on the remaining 8 cylinders. Thirty-five field tests were made over the three selected soil types, all fine-grained, using a 2-foot seismic line with hammer-impact points at 6-inch intervals. The small tack hammer and 5/8-inch steel ball was, again, used to develop seismic wave energy. Generally, the densities obtained from the velocity measurements were lower than those measured in the conventional field testing. Conclusions were reached that: (1) the method does not appear to be usable for measurement of density of essentially fine-grained soils when the moisture content greatly exceeds the optimum for compaction, and (2) due to a gradual reduction in velocity upon aging, apparently because of gradual absorption of pore water into the expandable interlayer region of the clay, the seismic test should be conducted immediately after soil compaction to obtain a meaningful velocity value.